cgroup: Fix race condition at rebind_subsystems()

mainline inclusion
from mainline-v6.0-rc3
commit 763f4fb7
category: bugfix
bugzilla: 187794, https://gitee.com/openeuler/kernel/issues/I5ZXVK
CVE: NA

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=763f4fb76e24959c370cdaa889b2492ba6175580

-------------------------------

Root cause:
The rebind_subsystems() is no lock held when move css object from A
list to B list,then let B's head be treated as css node at
list_for_each_entry_rcu().

Solution:
Add grace period before invalidating the removed rstat_css_node.
Reported-by: NJing-Ting Wu <jing-ting.wu@mediatek.com>
Suggested-by: NMichal Koutný <mkoutny@suse.com>
Signed-off-by: NJing-Ting Wu <jing-ting.wu@mediatek.com>
Tested-by: NJing-Ting Wu <jing-ting.wu@mediatek.com>
Link: https://lore.kernel.org/linux-arm-kernel/d8f0bc5e2fb6ed259f9334c83279b4c011283c41.camel@mediatek.com/T/Acked-by: NMukesh Ojha <quic_mojha@quicinc.com>
Fixes: a7df69b8 ("cgroup: rstat: support cgroup1")
Cc: stable@vger.kernel.org # v5.13+
Signed-off-by: NTejun Heo <tj@kernel.org>
Signed-off-by: NCai Xinchen <caixinchen1@huawei.com>
Reviewed-by: NGONG Ruiqi <gongruiqi1@huawei.com>
Reviewed-by: NWang Weiyang <wangweiyang2@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

kernel/cgroup/cgroup.c

@@ -1781,6 +1781,7 @@ int rebind_subsystems(struct cgroup_root *dst_root, u16 ss_mask)
 
 		if (ss->css_rstat_flush) {
 			list_del_rcu(&css->rstat_css_node);
+			synchronize_rcu();
 			list_add_rcu(&css->rstat_css_node,
 				     &dcgrp->rstat_css_list);
 		}